If you've mastered the art of Arduino, but haven't yet been brave enough to toss in a bit of GSM communication, the how-to guides linked below definitely deserve your attention.

The GSM Shield also includes a Telefonica SIM card that includes a worldwide data tariff which can be used anywhere there is a cellular signal.

This will allow the development platform to connect to the internet via GSM mobile phone networks. The module, or shield, was developed in conjunction with Telefónica’s Physical Internet Laboratory ...

Arduino devices have had the option of a GSM linkup for awhile, but getting that cellular link to truly strut its stuff hasn't always been easy, even for those of us who'd be inclined to program ...